A transceiver (i.e. transmitter and/or receiver), for example, a transceiver of a mobile communication device, typically comprises a signal processor, a power amplifier (PA) and a predistortion element of a power amplifier. In modern RF (Radio Frequency) transceiver systems, the reduction of current consumption is one of the most important design targets. The main sink of current in the transceiver chain is still the power amplifier, where much effort is spent in hardware design to achieve an acceptable compromise between current consumption and linearity over changing (environmental) conditions, e.g. temperature, frequency, load impedance. To further reduce the PA current consumption, the trend goes towards the implementation of adaptive (software) algorithms, which can overcome certain hurdles in hardware design. Examples for these algorithms are digital predistortion to increase the linear output power range, bias point adjustment to adapt the linearity according to the specification, or envelope tracking to adjust the power amplifier supply voltage with respect to the envelope of the input signal. The main target of such algorithms is to make use of the linearity-current trade-off and bring the PA as close as possible to the specification limit and to thus minimize the battery current.
The limited linearity of the PA causes so called amplitude-modulation-to-amplitude-modulation distortions (AM/AM-distortions) and so called amplitude-modulation-to-phase-modulation distortions (AM/PM-distortions). These AM/AM- and AM/PM-distortions are major concerns because they are responsible for intermodulation (IM) components and spectral regrowth. This may cause additional channel interferences to other communication channels. Additionally, effects of AM/AM- and AM/PM-distortions may cause in-band distortions that degrade the error vector magnitude (EVM).